The invention relates to a sensor for detecting an electrically conductive or magnetizable object with an oscillator comprising a resonant circuit including an inductance and a capacitance, the resonant circuit impedance depending on a damping distance between the inductance and the object and rising steeply in the range of small damping distances, further rising less steeply in the range of medium damping distances and substantially having a constant value in the range of large damping distances, and a closed adaptive loop stage supplying a loop current for the resonant circuit, this loop stage generating a course of an amplitude value dependent on the damping distance, and an evaluation circuit which detects an oscillator voltage applied to the resonant circuit.
Sensors of this type are known, for example, from European patent application 0 371 489.
In these sensors the response behavior depends on how the oscillator voltage applied to the resonant circuit is altered in response to the damping of the resonant circuit, i.e. in response to the damping distance of the object from the inductance. The course of the oscillator voltage over the damping distance is designated as characteristic curve of the oscillator, whereby only that part of the characteristic curve in which the oscillator voltage alters in response to the damping distance can be used for sensor tasks.
The European patent application 0 371 489 already describes a circuit, in which the part of the characteristic curve, in which the oscillator voltage alters with the damping distance, is extended, whereby in this circuit an extension of the characteristic curve takes place towards large damping distances and a behavior of the characteristic curve unfavorable for small damping distances, in particular any "breakdown" of the oscillator at small damping distances, is accepted.
Proceeding on the basis of the European patent application 0 371 489, the object underlying the invention is to improve a sensor of the generic type such that the oscillator also oscillates in the range of small damping distances and exhibits a characteristic curve, with which the oscillator voltage varies with the damping distance also in the range of small damping distances.